Now the city charter’s temporary prohibition on making changes to the ordinance is expiring, with the caveat that any alterations require a two-thirds majority of the City Council, or nine of 13 members.

The initiative’s lead backer, Brandon Rietheimer, has said the details of the voter-passed ordinance are in need of tweaks and fixes. But a draft plan that’s emerged from task force meetings would take a much bigger whack.

In short: Developers of new buildings and owners of existing large buildings in need of roof replacements would have far more options than adding a roof garden or solar panels. The draft outlines a complex set of alternatives geared toward reducing buildings’ greenhouse gas emissions, energy use and heat absorption.

So far, the proposed wide-scale changes, while dizzying to digest, are not giving Rietheimer heartburn. He’s mostly a fan of the draft plan.

“It basically tries to keep the benefits all the same, even if it’s achieved through different means,” said Rietheimer, the initiative’s campaign manager, on Friday. “In some ways we might be getting a bigger climate benefit than we would have initially.”

Meanwhile, developers and large-building owners contemplating roof replacements have been waiting to see what happens. The initiative’s impact has been mostly theoretical to this point, with no new “green roofs” built yet under the requirements.

The city is seeking public input on the draft plan until noon June 3. It organized a sparsely attended public briefing Friday and has a second session set for 9 a.m. Monday on the first floor of the Wellington E. Webb Municipal Office Building.

The task force — which represents wide-ranging interests, from the initiative’s authors to opponents in the building industry — is expected to finalize its proposed rewrite and send it to the council next month.

RJ Sangosti, The Denver Post

The Flight office building, at 3575 Ringsby Court in Denver, has included a green roof in its design. Photographed on May 9, 2018.

Here are the details of the draft plan

As with the voter-approved ordinance, the draft plan would apply only to new and existing buildings with at least 25,000 square feet of gross floor area inside. And residential buildings of up to four stories still would be exempt, while the draft plan adds in a new exemption for replacement roofs on existing buildings that are owned by nonprofits or officially designated as affordable housing, though those would have to convert to “cool” roofs. (More on those later.)

Here is a run-down of what developers and owners of large buildings can expect:

Green space: While they still could opt to install gardens, they’d have more options for doing so — including installing green space on terraces or on the ground, beyond what other city regulations require. Another option would be to pay into a city fund dedicated to expanding green space across the city, though this possibility has been greeted with skepticism from at least one council member.

Energy consumption: New and existing buildings, besides relying more heavily on solar energy generation (on- or off-site), could opt instead to install energy-efficiency building upgrades or achieve gold certification from the Leadership in Energy & Environmental Design (LEED) program.

“Cool” roofs: Regardless of which new options developers choose, however, the draft plan contains a fresh mandate. New buildings would be required to have “cool” roofs, which involve white or reflective roofing materials and coatings to significantly reduce heat absorption.

Roof replacements would have the most flexibility, with owners allowed to reduce other requirements by installing cool roof materials.

One complaint about the voter-passed rules is that because they set roof coverage proportions based on building square footage, large single-story industrial buildings and strip mall centers — whether under construction or in need of a roof replacement — face burdensome costs to comply.

The draft plan proposes a big shift to tiers based on buildings’ height. The basic calculations to set coverage areas for green roofs or solar arrays (if developers or owners chose those options) would be based on building height.

For instance, a full rooftop garden on a sprawling new one-story building would have to cover 10 percent of the roof space, or an equivalent space elsewhere. Required coverage areas range up to a maximum 60 percent of the roof space for buildings that are six stories or taller.

A green space that’s built as part of an existing building’s roof replacement would have to cover smaller spaces, ranging from 2 percent to 18 percent of the roof area, with the rest covered by cool-roof materials.

Within roughly the next decade, the largest existing buildings — those with 50,000 gross square feet or more — also would have to install on-site solar panels, seek LEED gold certification or meet energy-efficiency benchmarks as part of a new requirement.

RJ Sangosti, Denver Post file

Brandon Rietheimer, campaign manager for the Denver Green Roof Initiative, stands in the rooftop garden at the Ralph L. Carr Colorado Judicial Center on March 3, 2017. Denver voters passed Initiative 300 last week, requiring all new buildings of 25,000 square feet or larger to devote a portion of the roof to gardens and other green coverings that would absorb rainfall and reduce heat.

The proposed changes cut compliance costs

Building and real estate industry representatives unsuccessfully fought the Green Roof Initiative last fall. They have argued that Denver can achieve similar environmental goals without requiring costly rooftop gardens that are often inaccessible to the public.

Scenarios for new buildings found that the proposed mix of alternatives in the draft plan would cost from 20 percent to 90 percent less to implement, depending on building type, than requirements in the voter-passed ordinance. The upgrades would add 1 percent or less to the cost for some building projects, with others seeing slightly higher increases — but in most cases, the cost increase would be less than under the current ordinance for new construction.

“This proposal isn’t the ideal policy proposal for any one task force member,” said Katrina Managan, the energy-efficient buildings lead for the Denver Department of Public Health and Environment, during a council committee briefing May 7. “But this is something that they think is directionally going the right way, and once they get the details right, it’s hopefully something they can all accept. We’re working toward a consensus recommendation for you.”

But some voters who supported the initiative as a way to spur the building of more rooftop gardens are likely to view the proposed changes with suspicion, at least initially.

Rietheimer and some council members have praised the more complex approach as having the potential to be more effective than the original initiative.

“I think it upholds the intent pretty well — if not even better in some cases,” Rietheimer said.

Councilwoman Robin Kniech urged Managan during the committee meeting to emphasize that point over the cost benefits in the draft plan’s introduction so that people understand “that this will have the same or greater impact on climate protection.”

Asked Friday if he had any misgivings about the draft plan, Rietheimer replied: “I would like to see more green space than what we got. But at the end of the day, I think we made it more flexible, and I think we’re going to see more (environmentally friendly outcomes) across the city than we would have before.”

Jon Murray is an enterprise reporter on The Denver Post's government and politics team, with a focus on transportation. He previously covered Denver Mayor Michael Hancock and city government. A Colorado native, he joined The Denver Post in 2014 after reporting on city government and the legal system for The Indianapolis Star.